SDL::Tutorial::DrawingUser Contributed Perl DocumentaSDL::Tutorial::Drawing(3)NAMESDL::Tutorial::Drawing - basic drawing with Perl SDL
SYNOPSIS
# to read this tutorial
$ perldoc SDL::Tutorial::Drawing
# to create a bare-bones SDL app based on this tutorial
$ perl -MSDL::Tutorial::Drawing=basic_app.pl -e 1
DRAWING BASICS
As explained in SDL::Tutorial, all graphics in SDL live on a surface.
Consequently, all drawing operations operate on a surface, whether
drawing on it directly or blitting from another surface. The important
modules for this exercise are SDL::Rect and SDL::Color.
As usual, we'll start by creating a SDL::App object:
use SDL::App;
my $app = SDL::App->new(
-width => 640,
-height => 480,
-depth => 16,
);
Creating a New Surface with SDL::Rect
A SDL::Rect object is an SDL surface, just as an SDL::App object is.
As you'd expect, you need to specify the size of this object as you
create it. You can also specify its coordinates relative to the
origin.
Note: The origin, or coordinates 0, 0, is at the upper left of the
screen.
Here's how to create a square 100 pixels by 100 pixels centered in the
window:
use SDL::Rect;
my $rect = SDL::Rect->new(
-height => 100,
-width => 100,
-x => 270,
-y => 390,
);
This won't actually display anything yet, it just creates a rectangular
surface. Of course, even if it did display, you wouldn't see anything,
as it defaults to the background color just as $app does. That's where
SDL::Color comes in.
A Bit About Color
SDL::Color objects represent colors in the SDL world. These colors are
additive, so they're represented as mixtures of Red, Green, and Blue
components. The color values are traditionally given in hexadecimal
numbers. If you're exceedingly clever or really like the math, you can
figure out which values are possible by comparing them to your current
bit depth. SDL does a lot of autoconversion for you, though, so unless
extreme speed or pedantic detail are important, you can get by without
worrying too much.
Creating a color object is reasonably easy. As the color scheme is
additive, the lower the number for a color component, the less of that
color. The higher the number, the higher the component.
Experimentation may be your best bet, as these aren't exactly the
primary colors you learned as a child (since that's a subtractive
scheme).
Let's create a nice, full blue:
use SDL::Color;
my $color = SDL::Color->new(
-r => 0x00,
-g => 0x00,
-b => 0xff,
);
Note: The numbers are in hex; if you've never used hex notation in
Perl before, the leading "0x" just signifies that the rest of the
number is in base-16. In this case, the blue component has a value of
255 and the red and green are both zero.
Filling Part of a Surface
The "fill()" method of SDL::Surface fills a given rectangular section
of the surface with the given color. Since we already have a rect and
a color, it's as easy as saying:
$app->fill( $rect, $color );
That's a little subtle; it turns out that the SDL::Rect created earlier
represents a destination within the surface of the main window. It's
not attached to anything else. We could re-use it later, as necessary.
Updating the Surface
If you try the code so far, you'll notice that it still doesn't
display. Don't fret. All that's left to do is to call "update()" on
the appropriate surface. As usual, "update()" takes a Rect to control
which part of the surface to update. In this case, that's:
$app->update( $rect );
This may seem like a useless extra step, but it can be quite handy.
While drawing to the screen directly seems like the fastest way to go,
the intricacies of working with hardware with the appropriate timings
is tricky.
Working With The App
You can, of course, create all sorts of Rects with different sizes and
coordinates as well as varied colors and experiment to your heart's
content drawing them to the window. It's more fun when you can animate
them smoothly, though.
That, as usual, is another tutorial.
SEE ALSO
SDL::Tutorial
the basics of Perl SDL.
SDL::Tutorial::Animation
basic animation techniques
AUTHOR
chromatic, <chromatic@wgz.org>
Written for and maintained by the Perl SDL project,
<http://sdl.perl.org/>.
BUGS
No known bugs.
COPYRIGHT
Copyright (c) 2003 - 2004, chromatic. All rights reserved. This
module is distributed under the same terms as Perl itself, in the hope
that it is useful but certainly under no guarantee.
perl v5.14.1 2011-07-18 SDL::Tutorial::Drawing(3)
